Petty Officer Pamela Boehland says the 40-foot boat the Neptune hit an unknown object in the bay Friday night, leaving it with a 1-foot gash.
Boehland says the boat began taking on water and sinking. But a Coast Guard boat happened to be nearby, taking on board most of the Neptune's 22 passengers and crew and summoning another Coast Guard vessel that picked up the rest.
The boats took the passengers to San Francisco's Pier 39. There were no reports of injuries.
KGO-TV reported the passengers were celebrating a bachelor party when the accident occurred.
The station says the Coast Guard is trying to get the water out of The Neptune and will tow it back to port.
The Neptune's website, which advertises it as a "floating wine tasting room," says it holds 42 passengers for wine tasting.